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Q-angle undervalued? The relationship between Q-angle and medio-lateral position of the patella

PainSci summary of Herrington 2004

In 2004, this Manchester research group showed that abnormal patellar position tends to throw off Q-angle measurements. Specifically, if a Q-angle measurement is taken based on a patella that is displaced laterally, the result will not be as large as the real Q-angle.

original abstract

BACKGROUND: For an accurate quadriceps angle measurement, the patella must be centralised in the femoral trochlear groove, numerous authors have described lateral displacement of the patella in patellofemoral pain patients, this leads to the intriguing possibility that the Q-angle might be undervalued within patellofemoral pain patients who have laterally displaced patella.

INTERPRETATION: The adjusted Q-angle values for medially and neutral placed patellae brought the values very much into the centre of the reported ranges for Q-angles. After adjustment for lateral patella displacement, Q-angle values were towards the under end of values reported as normal, especially female values which were close to the previously reported pathological cut off point. Because of the inverse relationship between quadriceps strength and the magnitude of Q-angle and quadriceps crucial role in the aetiology of patellofemoral pain, any method which improves the reliability and applicability of Q-angle measurement could prove useful in investigations into the aetiology of and outcome from treatment of patellofemoral pain syndrome.

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